Application of octanohydroxamic acid for liquid-liquid extraction of manganese oxides and fabrication of supercapacitor electrodes

MnO₂ and Mn₃O₄ particles were prepared by wet chemical methods and efficiently dispersed and mixed with multiwalled carbon nanotubes (MWCNT) for the fabrication of composite MnO₂-MWCNT and Mn₃O₄-MWCNT electrodes for electrochemical supercapacitors (ES). The problem of particle agglomeration was addressed by particle extraction through a liquid-liquid interface (PELLI) using octanohydroxamic acid (OHA) as a new extractor. OHA exhibited remarkable adsorption on particles due to a bidentate bonding mechanism. The use of OHA broadened the application of PELLI technology, because it allowed good extraction of particles from an aqueous phase at high pH. Moreover, OHA allowed efficient extraction by strong adsorption on particles not only at the liquid-liquid interface, but also in the bulk of an aqueous phase. Building on the advantages offered by the PELLI method and OHA as an extractor we found that Mn₃O₄-MWCNT electrodes exhibited a remarkably high capacitance of 4.2F cm^-2. Another major finding was that capacitance of Mn₃O₄-MWCNT electrodes was higher than that of MnO₂-MWCNT electrodes at active mass of 33 mg cm^-2. This finding showed processing advantages of PELLI and paved the way for applications of novel colloidal and surface modification strategies for the development of advanced ES. A conceptually new approach has been proposed based on the use of hydroxamic acids as capping agents for synthesis and extractor molecules for PELLI.